package cryptotools

import (
	"crypto/aes"
	"crypto/cipher"
	"encoding/base64"
	"errors"
	"bytes"
	"time"
	"math/rand"
	"encoding/binary"
)

func GenerateInt32() (int32, []byte) {
	rand.Seed(time.Now().UnixNano())
	keyRoot := rand.Int()
	byteArray := make([]byte, 4)
	binary.BigEndian.PutUint32(byteArray, uint32(keyRoot))
	return int32(keyRoot), byteArray
} 

//pkcs7Padding 填充
func pkcs7Padding(data []byte, blockSize int) []byte {
    //判断缺少几位长度。最少1，最多 blockSize
    padding := blockSize - len(data)%blockSize
    //补足位数。把切片[]byte{byte(padding)}复制padding个
    padText := bytes.Repeat([]byte{byte(padding)}, padding)
    return append(data, padText...)
}

//pkcs7UnPadding 填充的反向操作
func pkcs7UnPadding(data []byte) ([]byte, error) {
    length := len(data)
    if length == 0 {
        return nil, errors.New("加密字符串错误！")
    }
    //获取填充的个数
    unPadding := int(data[length-1])
    return data[:(length - unPadding)], nil
}

//AesEncrypt 加密
func AES_Encrypt(data []byte, key []byte) ([]byte, error) {
    //创建加密实例
    block, err := aes.NewCipher(key)
    if err != nil {
        return nil, err
    }
    //判断加密快的大小
    blockSize := block.BlockSize()
    //填充
    encryptBytes := pkcs7Padding(data, blockSize)
    //初始化加密数据接收切片
    crypted := make([]byte, len(encryptBytes))
    //使用cbc加密模式
    blockMode := cipher.NewCBCEncrypter(block, key[:blockSize])
    //执行加密
    blockMode.CryptBlocks(crypted, encryptBytes)
    return crypted, nil
}

//AesDecrypt 解密
func AES_Decrypt(data []byte, key []byte) ([]byte, error) {
    //创建实例
    block, err := aes.NewCipher(key)
    if err != nil {
        return nil, err
    }
    //获取块的大小
    blockSize := block.BlockSize()
    //使用cbc
    blockMode := cipher.NewCBCDecrypter(block, key[:blockSize])
    //初始化解密数据接收切片
    crypted := make([]byte, len(data))
    //执行解密
    blockMode.CryptBlocks(crypted, data)
    //去除填充
    crypted, err = pkcs7UnPadding(crypted)
    if err != nil {
        return nil, err
    }
    return crypted, nil
}

//EncryptByAes Aes加密 后 base64 再加
func AES_Encrypt_Base64(data []byte, key []byte) (string, error) {
    res, err := AES_Encrypt(data, key)
    if err != nil {
        return "", err
    }
    return base64.StdEncoding.EncodeToString(res), nil
}

//DecryptByAes Aes 解密
func AES_Decrypt_Base64(data string, key []byte) ([]byte, error) {
    dataByte, err := base64.StdEncoding.DecodeString(data)
    if err != nil {
        return nil, err
    }
    return AES_Decrypt(dataByte, key)
}